THURSDAY, April 23 (HealthDay News) -- U.S. male military veterans exposed to the Agent Orange herbicide/defoliant are at increased risk for aggressive recurrence of prostate cancer, a new study finds.

It included 1,495 veterans who'd had surgery to remove cancerous prostates. Of those, the 206 men who'd been exposed to Agent Orange were nearly 50 percent more likely to develop an aggressive recurrence of their cancer, even though their disease seemed relatively non-aggressive at the time of surgery.

The study also found it took only eight months for prostate specific antigen (PSA) levels -- an indicator of cancer aggressiveness -- to double among the Agent Orange-exposed veterans with recurrent cancer, compared to more than 18 months among non-exposed veterans.

The study is published in the May issue of the British Journal of Urology International.

"There is something about the biology of these cancers that are associated with prior Agent Orange exposure that is causing them to be more aggressive. We need to get the word out," study corresponding author Dr. Martha Terris, chief of urology at the Charlie Norwood VA Medical Center in Augusta and professor of urology at the Medical College of Georgia School of Medicine, said in a school news release.

She said doctors treating prostate cancer patients who've been exposed to Agent Orange need to be aware that these patients may require closer monitoring and so-called salvage therapy quickly if their prostate cancer returns.

"Not only are their recurrence rates higher, but their cancers are coming back and growing much faster when they do come back," Terris said.

There's increasing evidence that exposure to Agent Orange, which was used during the Vietnam War, increases the risk for a number of health problems. Agent Orange contained a known carcinogen called dioxin, which is also found in herbicides and pesticides used by U.S. farmers, according to background information in the news release about the study.